DRW: Add new Draw Manager OpenGL Context.

This separate context allows two things:
- It allows viewports in multi-windows configuration.
- F12 render can use this context in a separate thread and do a non-blocking render.

The downside is that the context cannot be used while rendering so a request to refresh a viewport will lock the UI. This is something that will be adressed in the future.

Under the hood what does that mean:
- Not adding more mess with VAOs management in gawain.
- Doing depth only draw for operators / selection needs to be done in an offscreen buffer.
- The 3D cursor "autodis" operator is still reading the backbuffer so we need to copy the result to it.
- All FBOs needed by the drawmanager must to be created/destroyed with its context active.
- We cannot use batches created for UI in the DRW context and vice-versa. There is a clear separation of resources that enables the use of safe multi-threading.

7 files changed, 34 insertions, 4 deletions

diff --git a/source/blender/gpu/CMakeLists.txt b/source/blender/gpu/CMakeLists.txt
index 189ca8e6a33..5c0115d967a 100644
--- a/source/blender/gpu/CMakeLists.txt
+++ b/source/blender/gpu/CMakeLists.txt
@@ -150,6 +150,7 @@ data_to_c_simple(shaders/gpu_shader_image_modulate_alpha_frag.glsl SRC)
 data_to_c_simple(shaders/gpu_shader_image_alpha_color_frag.glsl SRC)
 data_to_c_simple(shaders/gpu_shader_image_color_frag.glsl SRC)
 data_to_c_simple(shaders/gpu_shader_image_depth_linear_frag.glsl SRC)
+data_to_c_simple(shaders/gpu_shader_image_depth_copy_frag.glsl SRC)
 data_to_c_simple(shaders/gpu_shader_image_interlace_frag.glsl SRC)
 data_to_c_simple(shaders/gpu_shader_3D_image_vert.glsl SRC)
 data_to_c_simple(shaders/gpu_shader_3D_vert.glsl SRC)
diff --git a/source/blender/gpu/GPU_batch.h b/source/blender/gpu/GPU_batch.h
index d2f3409dc07..5807af7b359 100644
--- a/source/blender/gpu/GPU_batch.h
+++ b/source/blender/gpu/GPU_batch.h
@@ -58,6 +58,8 @@ void gpu_batch_init(void);
 void gpu_batch_exit(void);
 
 /* gpu_batch_presets.c */
+/* Only use by draw manager. Use the presets function instead for interface. */
+Gwn_Batch *gpu_batch_sphere(int lat_res, int lon_res) ATTR_WARN_UNUSED_RESULT;
 /* Replacement for gluSphere */
 Gwn_Batch *GPU_batch_preset_sphere(int lod) ATTR_WARN_UNUSED_RESULT;
 Gwn_Batch *GPU_batch_preset_sphere_wire(int lod) ATTR_WARN_UNUSED_RESULT;
diff --git a/source/blender/gpu/GPU_shader.h b/source/blender/gpu/GPU_shader.h
index ca6e8343401..def0b0bfbc7 100644
--- a/source/blender/gpu/GPU_shader.h
+++ b/source/blender/gpu/GPU_shader.h
@@ -134,6 +134,7 @@ typedef enum GPUBuiltinShader {
 	GPU_SHADER_2D_IMAGE_MASK_UNIFORM_COLOR,
 	GPU_SHADER_3D_IMAGE_MODULATE_ALPHA,
 	GPU_SHADER_3D_IMAGE_DEPTH,
+	GPU_SHADER_3D_IMAGE_DEPTH_COPY,
 	/* stereo 3d */
 	GPU_SHADER_2D_IMAGE_INTERLACE,
 	/* points */
diff --git a/source/blender/gpu/intern/gpu_batch_presets.c b/source/blender/gpu/intern/gpu_batch_presets.c
index 9db04832a51..21d6906083a 100644
--- a/source/blender/gpu/intern/gpu_batch_presets.c
+++ b/source/blender/gpu/intern/gpu_batch_presets.c
@@ -31,6 +31,7 @@
 
 #include "BLI_utildefines.h"
 #include "BLI_math.h"
+#include "BLI_threads.h"
 
 #include "GPU_batch.h"
 #include "gpu_shader_private.h"
@@ -71,7 +72,7 @@ static void batch_sphere_lat_lon_vert(
 }
 
 /* Replacement for gluSphere */
-static Gwn_Batch *batch_sphere(int lat_res, int lon_res)
+Gwn_Batch *gpu_batch_sphere(int lat_res, int lon_res)
 {
 	const float lon_inc = 2 * M_PI / lon_res;
 	const float lat_inc = M_PI / lat_res;
@@ -146,6 +147,7 @@ static Gwn_Batch *batch_sphere_wire(int lat_res, int lon_res)
 Gwn_Batch *GPU_batch_preset_sphere(int lod)
 {
 	BLI_assert(lod >= 0 && lod <= 2);
+	BLI_assert(BLI_thread_is_main());
 
 	if (lod == 0) {
 		return g_presets_3d.batch.sphere_low;
@@ -161,6 +163,7 @@ Gwn_Batch *GPU_batch_preset_sphere(int lod)
 Gwn_Batch *GPU_batch_preset_sphere_wire(int lod)
 {
 	BLI_assert(lod >= 0 && lod <= 1);
+	BLI_assert(BLI_thread_is_main());
 
 	if (lod == 0) {
 		return g_presets_3d.batch.sphere_wire_low;
@@ -182,9 +185,9 @@ void gpu_batch_presets_init(void)
 	}
 
 	/* Hard coded resolution */
-	g_presets_3d.batch.sphere_low = batch_sphere(8, 16);
-	g_presets_3d.batch.sphere_med = batch_sphere(16, 10);
-	g_presets_3d.batch.sphere_high = batch_sphere(32, 24);
+	g_presets_3d.batch.sphere_low = gpu_batch_sphere(8, 16);
+	g_presets_3d.batch.sphere_med = gpu_batch_sphere(16, 10);
+	g_presets_3d.batch.sphere_high = gpu_batch_sphere(32, 24);
 
 	g_presets_3d.batch.sphere_wire_low = batch_sphere_wire(6, 8);
 	g_presets_3d.batch.sphere_wire_med = batch_sphere_wire(8, 16);
diff --git a/source/blender/gpu/intern/gpu_shader.c b/source/blender/gpu/intern/gpu_shader.c
index c25d03dff2f..b06ee56c21f 100644
--- a/source/blender/gpu/intern/gpu_shader.c
+++ b/source/blender/gpu/intern/gpu_shader.c
@@ -77,6 +77,7 @@ extern char datatoc_gpu_shader_image_interlace_frag_glsl[];
 extern char datatoc_gpu_shader_image_mask_uniform_color_frag_glsl[];
 extern char datatoc_gpu_shader_image_modulate_alpha_frag_glsl[];
 extern char datatoc_gpu_shader_image_depth_linear_frag_glsl[];
+extern char datatoc_gpu_shader_image_depth_copy_frag_glsl[];
 extern char datatoc_gpu_shader_3D_vert_glsl[];
 extern char datatoc_gpu_shader_3D_normal_vert_glsl[];
 extern char datatoc_gpu_shader_3D_flat_color_vert_glsl[];
@@ -712,6 +713,8 @@ GPUShader *GPU_shader_get_builtin_shader(GPUBuiltinShader shader)
 		                                         datatoc_gpu_shader_image_modulate_alpha_frag_glsl },
 		[GPU_SHADER_3D_IMAGE_DEPTH] = { datatoc_gpu_shader_3D_image_vert_glsl,
 		                                datatoc_gpu_shader_image_depth_linear_frag_glsl },
+		[GPU_SHADER_3D_IMAGE_DEPTH_COPY] = { datatoc_gpu_shader_3D_image_vert_glsl,
+		                                     datatoc_gpu_shader_image_depth_copy_frag_glsl },
 
 		[GPU_SHADER_2D_IMAGE_INTERLACE] = { datatoc_gpu_shader_2D_image_vert_glsl,
 		                                    datatoc_gpu_shader_image_interlace_frag_glsl },
diff --git a/source/blender/gpu/intern/gpu_viewport.c b/source/blender/gpu/intern/gpu_viewport.c
index fc045805874..83b9a8f0b0e 100644
--- a/source/blender/gpu/intern/gpu_viewport.c
+++ b/source/blender/gpu/intern/gpu_viewport.c
@@ -345,6 +345,8 @@ void GPU_viewport_bind(GPUViewport *viewport, const rcti *rect)
 	int rect_w = BLI_rcti_size_x(rect) + 1;
 	int rect_h = BLI_rcti_size_y(rect) + 1;
 
+	DRW_opengl_context_enable();
+
 	if (dfbl->default_fb) {
 		if (rect_w != viewport->size[0] || rect_h != viewport->size[1] || U.ogl_multisamples != viewport->samples) {
 			gpu_viewport_buffers_free(
@@ -465,6 +467,7 @@ cleanup:
 		if (!ok) {
 			GPU_viewport_free(viewport);
 			MEM_freeN(viewport);
+			DRW_opengl_context_disable();
 			return;
 		}
 
@@ -523,7 +526,11 @@ void GPU_viewport_unbind(GPUViewport *viewport)
 	if (dfbl->default_fb) {
 		GPU_framebuffer_texture_unbind(NULL, NULL);
 		GPU_framebuffer_restore();
+	}
 
+	DRW_opengl_context_disable();
+
+	if (dfbl->default_fb) {
 		glEnable(GL_SCISSOR_TEST);
 		glDisable(GL_DEPTH_TEST);
 	}
@@ -581,6 +588,7 @@ static void gpu_viewport_passes_free(PassList *psl, int psl_len)
 	}
 }
 
+/* Must be executed inside Drawmanager Opengl Context. */
 void GPU_viewport_free(GPUViewport *viewport)
 {
 	gpu_viewport_engines_data_free(viewport);
diff --git a/source/blender/gpu/shaders/gpu_shader_image_depth_copy_frag.glsl b/source/blender/gpu/shaders/gpu_shader_image_depth_copy_frag.glsl
new file mode 100644
index 00000000000..10f4dfd5a87
--- /dev/null
+++ b/source/blender/gpu/shaders/gpu_shader_image_depth_copy_frag.glsl
@@ -0,0 +1,12 @@
+
+in vec2 texCoord_interp;
+out vec4 fragColor;
+
+uniform sampler2D image;
+
+void main()
+{
+	float depth = texture(image, texCoord_interp).r;
+	fragColor = vec4(depth);
+	gl_FragDepth = depth;
+}